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TRANSCRIPT
Full Moment Tensor Inversion as a Practical Tool in Case of Discrimination of Tectonic
and Anthropogenic Seismicity in Poland
GRZEGORZ LIZUREK1
Abstract—Tectonic seismicity in Poland is sparse. The biggest
event was located near Myslenice in 17th century of magnitude 5.6.
On the other hand, the anthropogenic seismicity is one of the
highest in Europe related, for example, to underground mining in
Upper Silesian Coal Basin (USCB) and Legnica Głogow Copper
District (LGCD), open pit mining in ‘‘Bełchatow’’ brown coal mine
and reservoir impoundment of Czorsztyn artificial lake. The level
of seismic activity in these areas varies from tens to thousands of
events per year. Focal mechanism and full moment tensor (MT)
decomposition allow for deeper understanding of the seismogenic
process leading to tectonic, induced, and triggered seismic events.
The non-DC components of moment tensors are considered as an
indicator of the induced seismicity. In this work, the MT inversion
and decomposition is proved to be a robust tool for unveiling
collapse-type events as well as the other induced events in Polish
underground mining areas. The robustness and limitations of the
presented method is exemplified by synthetic tests and by analyz-
ing weak tectonic earthquakes. The spurious non-DC components
of full MT solutions due to the noise and poor focal coverage are
discussed. The results of the MT inversions of the human-related
and tectonic earthquakes from Poland indicate this method as a
useful part of the tectonic and anthropogenic seismicity discrimi-
nation workflow.
Key words: Anthropogenic seismicity, moment tensor, focal
mechanism, induced seismicity, intraplate seismicity.
1. Introduction
Earthquakes seldom happen in Poland and earth-
quakes large enough to cause damage are even more
rare. About 100 accounts of earthquakes are known
from Polish history, starting from the year 1000 A.D.
Most of the felt earthquakes took place in the
Southern Poland (Fig. 1). The greatest earthquake in
Poland is considered to be the event of December 3,
1786 that has taken the biggest event was estimated at
5.6. The Podhale earthquake from 30th November
2004 ML = 4.8 was the biggest earthquake located in
Poland since the instrumental measurements started.
(Wiejacz and Debski 2009). Smaller earthquakes
were also observed near Krynica: (Guterch et al.
2005; Plesiewicz and Wiszniowski 2015). The last
significant tectonic earthquakes in Poland were
located in the Tornquist-Teisseyre zone, where seis-
mic activity was reported in the past (e.g. Guterch
2009), but only the 2007, ML = 2.8 and 2012,
ML = 3.8 seismic events located near Jarocin were
recorded (Lizurek et al. 2013). The moment tensor
solutions were obtained for the strongest event from
Podhale and both Jarocin earthquakes. Map of sig-
nificant historical earthquakes as well as those
recorded instrumentally is shown on Fig. 1.
Main sources of the seismic activity in Poland are
industrial activities: underground mining in Upper
Silesian Coal Basin (USCB) and Legnica Głogow
Copper District (LGCD), open pit mining in ‘‘Beł-
chatow’’ brown coal mine and reservoir
impoundment of Czorsztyn artificial lake near
Niedzica hydropower plant (Fig. 1). Seismic activity
in USCB (Southern Poland) is very high, there are
about 3000 events per year recorded by Polish Seis-
mological Network run by Institute of Geophysics,
Polish Academy of Sciences. Moreover, there are
about 200 events of ML C2.4 annually, and 55 900
events of ML C1.5 occurred over the period
1974–2005 according to Upper Silesian Seismologi-
cal Network run by Central Mining Institute. There
were six large events with 3.8 B ML B 4.2 since
1992 till 2015 (Stec 2007; Marcak and Mutke 2013).
The focal mechanisms of significant USCB events are
1 Institute of Geophysics, Polish Academy of Sciences, ul.
Ks. Janusza 64, 01-452 Warsaw, Poland. E-mail:
Pure Appl. Geophys. 174 (2017), 197–212
� 2016 The Author(s)
This article is published with open access at Springerlink.com
DOI 10.1007/s00024-016-1378-9 Pure and Applied Geophysics
available in: Gibowicz and Wiejacz (1994), Gibowicz
et al. (1996), Marcak and Mutke (2013), Stec (2007).
The anthropogenic seismic activity of LGCD (SW
Poland) is related to the copper ore underground
exploitation in 3 mines: ‘‘Rudna’’, ‘‘Polkowice-
Sieroszowice’’, and ‘‘Lubin’’. These mines produce
annually several hundreds of seismic events with
local magnitude in the range 0.4–4.5 (Lasocki 2005).
The largest events in this area were ML = 4.5 from
March 24th 1977 (Gibowicz et al. 1979) and
ML = 4.3 from June 20th 1987 (Gibowicz et al.
1989) both located within ‘‘Lubin’’ mine, and
ML = 4.2 from March 19th 2013 located in ‘‘Rudna’’
mine (Lizurek et al. 2015; Rudzinski et al. 2016).
Moment tensor solutions for most of the significant
events are available (e.g. Gibowicz et al. 1989;
Lizurek et al. 2015; Orlecka-Sikora et al. 2014).
Open pit brown coal mining in the Bełchatow area
(Central Poland) causes lower seismicity than the
underground mining, There are about 60 events
recorded by PLSN annually, but 4 events since
opening of the mine in 1977 (Gibowicz et al. 1982)
had magnitude ML C 4. The largest event in this area
took place on November 29, 1980 M4.6, the latest
event of magnitude above M4 took place on January
22, 2010 (Wiejacz and Rudzinski 2010). The last
anthropogenic seismic activity is linked to the
impoundment of Czorsztyn artificial lake. The lake
was created by backing up water by an earth dam of
the hydropower plant Niedzica on Dunajec river,
southern Poland (Fig. 1). It’s filling ended in 1997.
The reservoir of 234.5 million cubic meters capacity
is shallow, on average between 20 to 50 m of water
column. Between 1995 and 2011 there was only one
Figure 1Anthropogenic seismicity areas in Poland on the background of the tectonic seismicity map. Triangle denotes USCB, rectangle denotes
LGCD, ellipse marks the Bełchatow open pit and black circle denotes Czorsztyn Lake area. Stars denote instrumentally recorded events in
Poland (gray ones for Jarocin earthquakes, yellow for Podhale, and red for Krynica events, blue is the strongest felt event from Kaliningrad),
white circles denote historical earthquakes with not well-constrained location, filled circles denote historical earthquakes with well-
constrained location. Podhale event MT in the last row is taken from Wiejacz and Debski (2009)
198 G. Lizurek Pure Appl. Geophys.
event recorded in this area, but since November 2011
seismic activity increased up to about several events
per month. The seismicity of the area is considered as
the triggered seismicity case (Białon et al. 2015).
Currently there are over 150 events located in this
area with ML from -0.6 to 2.4. There are 23 moment
tensor solutions calculated for the events of
0.2 B ML B 2.1.
The moment tensor (MT) inversion confirmed its
importance by allowing to interpret the MT solutions
in terms of the dominant stress orientation in the
seismic active regions (Hardebeck and Michael 2006)
and as one of the main tools to investigate the faulting
mechanisms of the significant earthquakes (Ekstrom
et al. 2012) as well as the local tectonic seismicity
(e.g., Cesca et al. 2006). Full MT inversion is con-
sidered as a useful method of investigation of the
volcanic, anthropogenic, and other exotic seismic
sources (e.g., Cesca et al. 2008; Gibowicz and Kijko
1994; Vavrycuk and Kim 2014; Heimann et al. 2013).
Full MT decomposition allows for deeper under-
standing of the seismogenic process leading to
induced and triggered seismic events (e.g., Fletcher
and McGarr 2005; Ford et al. 2009). The non-DC
component of focal mechanism solution was con-
sidered as an indicator of the induced seismicity since
1980’s by several authors (e.g., Teisseyre 1980;
Rudajev and Sıleny 1985), recently the non-DC
component of the MT decomposition is proposed as
such indicator (Cesca et al. 2013). Moreover, rec-
ommendation for discrimination of anthropogenic
and natural seismicity included use of MT inversion
in the complex investigation procedure described in
Dahm et al. (2013). The authors of the latter work
also discriminate between triggered and induced
anthropogenic seismicity. The procedure of discrim-
ination between natural and anthropogenic, and also
between induced and triggered seismicity takes into
account a physics-based probabilistic approach as
well as the statistics-based seismicity model and
source parameter approach. The latter was dedicated
mainly into the collapse-type events. In this work the
MT decomposition for pure shearing (DC) non-
shearing components: isotropic (ISO) and compen-
sated linear vector dipole (CLVD) is proved to be
robust tool for unveiling collapse-type events as well
as the other purely induced events both in USCB and
LGCD. Nevertheless, the limitation of the method-
ology of the P-wave first pulse displacement
amplitude is also shown upon the synthetic test. The
results of the MT inversions of the human-related and
tectonic earthquakes from Poland indicate this
method as useful part of the discrimination workflow,
but it cannot be treated as the main and only input for
such discrimination.
2. Methodology of moment tensor inversion
Moment tensors are obtained by inversion of the
P-wave amplitudes in time domain (Wiejacz 1992;
Kwiatek and Martinez-Garzon 2016). According to
Fitch et al. (1980), De Natale et al. (1987) and Aki
and Richards (2002), the recorded displacement for
the P-wave phase is:
UP x; tð Þ ¼c � _M t � r
a
� �� c
4pqa3rl; ð1Þ
where q is the average medium density, r is the
source-receiver distance, a is the average velocity of
the P-wave, M is the seismic moment tensor, l is the
P-wave direction at the receiver, and c is the P-wave
direction at the source.
Moment tensor is obtained by solving of a set of N
equations of type (1), where N is the number of sta-
tions that recorded the event. Six independent
components of moment tensor require minimum of
six equations, but the more the better. The system of
Eqs. (1) is overdetermined and solved for using a
least-squares approach (L2 norm) with the cost
function being the sum of squares of residuals. When
the condition of the zero trace is imposed on the
solution, the deviatoric moment tensor may be
determined, which excludes mechanism with volu-
metric change in source. When the conditions of the
zero trace and zero determinant are set, the solution is
limited to the double-couple source. The full moment
solution can also be decomposed into the isotropic
(ISO), compensated linear vector dipole (CLVD) and
double-couple (DC) parts of the mechanism follow-
ing the default decomposition scheme of Knopoff and
Randall (1970) with percentage of decomposed ten-
sor elements calculated by either Knopoff and
Randall (1970) or Vavrycuk (2001, 2015). This
Vol. 174, (2017) Full Moment Tensor Inversion as a Practical Tool 199
decomposition shows usually complexity of the
source process and is used to check the quality of the
solution (Wiejacz 1992). Uncertainties of the esti-
mated moment tensors can be estimated through the
normalized root-mean-square (RMS) error between
theoretical and estimated amplitudes (Stierle et al.
2014a, b):
RMS ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiPNi¼1ðUmeasured
i � Uthi Þ
2
PNi ðUmeasured
i Þ2
s
: ð2Þ
All of the studied MT solutions in this work were
obtained with above described method. Nevertheless,
not for all of them the uncertainty estimates are
available.
3. Moment tensor solutions of tectonic earthquakes
Moment tensor solutions of three tectonic events
are available in Poland; event from Podhale and two
events from Jarocin (Table 1). Full moment tensors
(full MT), deviatoric (trace-null MT), and double-
couple (DC MT) solutions were calculated for Jarocin
earthquakes, while in case of Podhale there were full
and DC solutions available. The Podhale earthquake
full MT was obtained with 19 regional broadband
stations (Wiejacz and Debski 2009). The decompo-
sition of the full MT following Knopoff and Randall
(1970) approach shows very small non-DC part in the
focal mechanism, which is expected in case of the
tectonic earthquakes.
The two Jarocin events were recorded at different
sets of stations. The 2007 Jarocin event was recorded
at 12 good quality recordings available from the
PLSN and PASSEQ broadband stations. The epi-
central distance varied from 40 to 260 km. Most of
the stations were local stations from the PASSEQ
project (Wilde-Piorko et al. 2008), only two stations
were the PLSN broadband ones (OJC and KSP). The
2012 earthquake was recorded at 15 stations of PLSN
and VEBSN (Virtual European Broadband Seismic
Network), temporary mobile seismic monitoring
network, ‘‘ _Zelazny Most’’ repository lake temporary
monitoring short period network and one station from
the Bełchatow Mine local network. The azimuthal
coverage was worse than in case of the 2007 event.
The NW quadrant had only one station, namely GKP.
The epicentral distance varied from 110 to 430 km,
with most of the stations located about 200 km or
further from source. The 2007 Jarocin event results
show almost 40 % of non-DC components and the
2012 full MT has an unrealistically high non-DC
component with negligible DC part of the mecha-
nism. Such solution may be a result of the noisy data,
improper velocity model or the anisotropy of the
rocks. In case of tectonic earthquakes, the non-DC
Table 1
Moment tensor solutions of tectonic earthquakes in Poland
Event November 30, 2004, Podhale May 6, 2007, Jarocin January 6, 2012, Jarocin
Magnitude ML 4.8 2.8 3.8
Location
Longitude (8) 19.899 17.496 17.533
Latitude (8) 49.445 52.009 52.007
MT components (Nm)
M11 1.03 9 1015 3.81 9 1012 4.82 9 1016
M22 -2.75 9 1015 1.93 9 1012 4.82 9 1016
M33 -3.78 9 1015 -8.08 9 1012 -4.98 9 1016
M12 2.08 9 1015 -2.27 9 1012 4.21 9 1013
M13 1.54 9 1015 -5.27 9 1012 -1.51 9 1013
M23 2.68 9 1015 0.97 9 1012 -4.53 9 1012
MT decomposition
ISO (%) -2 -7.7 19.2
CLVD (%) 2.4 -30.1 -80.7
DC (%) 95.6 62.2 0.1
Parameters of Podhale event from Wiejacz and Debski (2009)
200 G. Lizurek Pure Appl. Geophys.
components are considered as a result of anisotropy
of the rocks. Even pure shear faulting the non-DC
values derived from full moment tensor solution can
reach up to 30 % (Vavrycuk 2005; Davi and Vavry-
cuk 2012). On the other hand, the non-DC
components obtained in the amplitude inversion can
be a product of noisy data and effect of the poor
coverage of focal sphere Wiejacz (1992). The latter
seems to be the case of the full MT inversions of the
Jarocin events, where 12 and 15 stations were avail-
able, and focal coverage was limited (Fig. 2).
Moreover, the 1D velocity model in case of regional
epicentral distances in Poland seems to be very
general approximation (Rudzinski et al. 2016) and
due to the complex geology of Poland it may be the
source of the errors. It is proved that Tornquist–
Teisseyre zone influence the S-wave splitting (Wie-
jacz 2001). Detailed analysis of the full, deviatoric
and pure DC solutions of both Jarocin events unveil,
that deviatoric solutions show the DC component as
the main part of the mechanism in both cases in
contrary to the full MT solution of the 2012 event.
(Table 2).
The synthetic tests of the focal coverage and noise
influence on the results of full MT solutions were
carried out to investigate the reliability of the full MT
result. Synthetic amplitudes and polarities were
generated for a priori known fault orientation—
Figure 2Full moment tensor solutions of Jarocin 2007 (left) and 2012 (right) earthquakes with stations and all possible nodal plane solutions
Table 2
Moment tensor solutions of Jarocin earthquakes
Event May 6, 2007, Jarocin January 6, 2012, Jarocin
Full MT Null-trace MT Full MT Null-trace MT
MT components (Nm)
M11 3.81 9 1012 3.17 9 1012 4.82 9 1016 1.81 9 1013
M22 1.93 9 1012 1.75 9 1012 4.82 9 1016 5.37 9 1013
M33 -8.08 9 1012 -4.92 9 1012 -4.98 9 1016 -7.19 9 1013
M12 -2.27 9 1012 -2.12 9 1012 4.21 9 1013 4.00 9 1013
M13 -5.27 9 1012 -5.09 9 1012 -1.51 9 1013 -1.55 9 1013
M23 0.97 9 1012 1.10 9 1012 -4.53 9 1012 -0.56 9 1013
RMS error 0.39 0.40 0.49 0.50
MT decomposition
ISO (%) -7.7 – 19.2 –
CLVD (%) -30.1 -16.6 -80.7 15.7
DC (%) 62.2 83.4 0.1 84.3
Vol. 174, (2017) Full Moment Tensor Inversion as a Practical Tool 201
vertical fault with strike N–E. The synthetic input
data were amplitude and polarities of displacement
following the proper focal sphere quadrants to the
configuration with the maximum amplitudes follow-
ing the P and T axes for the assumed fault. The RMS
error of all MT solutions for such prepared synthetics
was smaller than 0.01. First, test was run with 16
stations covering uniformly all azimuthal range with
22.5 degrees between every station. Second, the take-
off angles were set to cover well the focal sphere
(Fig. 3). In both cases, the jacknife station rejection
test and bootstrap amplitude resampling tests were
conducted. In case of the jacknife test, the seismic
moment tensor inversion was performed using all
available stations. Then, the inversion was performed
16 times and each time different station was removed
before inversion was performed. In amplitude
resampling procedure, the random noise was
introduced to input amplitude data. The amount of
noise added to the original amplitude was specified as
a random number drawn from Gaussian distribution
with mean 0 and standard deviation of 0.1, 0.3, and
0.5. The noise to input amplitude data reached a
factor of 0.2, 0.6, and 1, respectively. The number of
bootstrap samples was 100, which generated 100
resampled moment tensors (Kwiatek and Martinez-
Garzon 2016). Since the noise experiment is only
made for amplitudes, it doesn’t take into account
contamination of the whole seismogram by a noise.
In a high noise contamination, also the arrival time of
the maximum amplitude could be missed and the
damaging effect of the noise could be enhanced.
Results of the jacknife test show that the influence
of a single station on MT decomposition is moderate
(Table 3), while in case of the nodal plane orientation
is almost negligible (Fig. 4, upper row), even if the
Figure 3Vertical fault with strike N-S geometry used in the testing procedure. Black dots denote the positive polarities and white dots denote negative
polarities. Left beach-ball shows the same take-off angles on all stations, right beach-ball shows good focal coverage of stations, both network
configurations were used in synthetic tests
Table 3
Results of Jacknife tests of station on P-wave amplitude MT inversion
Double-couple solution Null-trace solution Full solution
RMS DC (%) RMS DC (%) CLVD
(%)
RMS DC (%) CLVD
(%)
ISO (%)
Poor focal sphere
coverage
0.009–0.01 100 4 9 10-7–5 9 10-7 99.9–100 0–0.1 4 9 10-7–0.02 84–100 -12 to 0 0–4
Good focal sphere
coverage
0.009–0.01 100 4 9 10-7–6 9 10-7 99.9–100 0–0.1 4 9 10-7–6 9 10-7 99.9–100 0 to 0.1 0–0.1
202 G. Lizurek Pure Appl. Geophys.
take-off angles are similar or equal. The non-DC
components of the solutions were up to 16 % in case
of poor focal sphere coverage in the full MT solution
but only up to 0.1 in the null-trace solution. In case of
good focal sphere coverage the non-DC components
in both full and null-trace solutions are negligible.
The nodal plane orientation is not influenced by the
single station in all tests.
The bootstrap amplitude resampling test results
show the take-off angle and focal sphere coverage
role in full MT inversion of noisy data (Figs. 5, 6;
Table 4). The obtained DC components of MT are
negligibly small in case of vast majority of the
solutions obtained for the same take-off angle con-
figuration. Variability of the P and T axes is high
and highly noise dependent—the higher noise
applied the higher variability in P and T axes ori-
entation (Fig. 5). The non-DC components are
retrieved badly even in case of small noise con-
tamination of the input data. The influence of the
amplitude noise amount is significant, but there is a
decrease of the solutions with DC of 50 % and
above (Fig. 6) for the higher noise contamination. In
contrary, the DC component is dominant in case of
trace-null solution. On the other hand, the DC
components in case of good focal sphere coverage
showed the dominance of the DC component in
solution even when up to 100 % noise was applied
(Fig. 6). The null-trace solutions are in agreement
with full MT solutions in terms of DC component
for the good focal sphere coverage configuration.
The RMS error estimates don’t differ much for both
configurations, but obviously the bigger noise
applied the higher RMS errors. However, even in
case high noise contamination of the input data the
RMS didn’t exceed the 0.3 value.
Figure 4Results of the jacknife station rejection test. Upper row represents the results of tests for network configuration with the uniform take-off angle
on all azimuths. The lower row represents network configuration with the different take-off angles covering the focal sphere well
Vol. 174, (2017) Full Moment Tensor Inversion as a Practical Tool 203
The nodal plane orientation stability for full
(Fig. 5), deviatoric (Fig. 7), and DC (Fig. 8) solutions
was tested. The stability of nodal plane orientation was
very bad in case of full MT inversion for poor focal
sphere coverage even when small amount of noise was
contaminating the input data (Fig. 5, upper row). It is
connected with negligible DC part of the solution in
most of the cases. The deviatoric (Fig. 7) and DC
(Fig. 8) solutions were much more stable in obtaining
of the proper nodal plane orientation, the difference
between strike of the assumed fault planes and result-
ing ones were not higher than 10 degrees. In case of
good focal sphere coverage the stability of the nodal
plane is good for all types of solutions and wasn’t
influenced much by noise.
These results indicate that the Jarocin 2012
earthquake full MT solution was not reliable due to
poor focal sphere coverage and noise. On the
contrary the 2007 Jarocin event was much more
reliable, because the azimuthal and focal sphere
coverage was good. The difference comes from the
availability of local stations from PASSEQ epicen-
tral distance of which varies from 40 to 150 km. In
such case the ray tracing in the local velocity model
was possible and produced good range of the take-
off angles to cover well the focal sphere. Moreover,
the closer stations have usually higher signal-to-
noise ratio, which means lower noise contamination
of the data. The 2012 event analysis was limited to
the regional stations with the epicentral distance
from 110 to 430 km, which did not allow us to use
local velocity models in reliable way. The regional
variation of the global model used in ray tracing
procedure produced almost the same take-off angles
for all stations within the epicentral distance from
100 to 500 km. Therefore, in case of the MT
Figure 5Full MT results of the bootstrap amplitude resampling test. Upper row represents the results of tests for network configuration with the
uniform take-off angle on all azimuths. The lower row represents network configuration with the different take-off angles. Blue and red dots
represent tension and pressure axes, respectively. On the lower row the nodal planes are also denoted, while on the upper row there are only
principal axes shown due to the very small DC part of the solutions
204 G. Lizurek Pure Appl. Geophys.
inversion of small earthquakes and distant stations
the results should be carefully interpreted and tested
for the inconsistency between the full MT and null-
trace solutions. On the other hand, the deviatoric
and DC solutions are usually stable and reliable in
terms of the nodal planes orientations and seismic
moment component values.
4. Moment tensor solutions of anthropogenic
earthquakes
Anthropogenic seismicity is the main feature of
the overall seismic activity in Poland. There are
several tens of moment tensor mechanisms calculated
for events recorded locally in underground mines
Figure 6Histograms of the DC component of full and deviatoric MT solutions for all inversions carried out during bootstrap amplitude resampling test
Vol. 174, (2017) Full Moment Tensor Inversion as a Practical Tool 205
Table 4
Results of bootstrap tests of noise influence on P-wave amplitude MT inversion
Double-couple
solution
Null-trace solution Full solution
RMS DC
(%)
RMS DC (%) CLVD (%) RMS DC (%) CLVD (%) ISO (%)
Poor focal coverage (up to 20 %
noise)
0.02–0.06 100 0.01–0.05 92.8–100 -7.2 to 7.2 0.01–0.04 0.02–99.9 -67.9 to
67.9
-32.1 to
32.1
Good focal coverage (up to 20 %
noise)
0.02–0.06 100 0.01–0.05 96.1–100 -3.5 to 3.9 0.01–0.05 94.5–100 -3.5 to 4 -1.2 to 1.5
Poor focal coverage (up to 60 %
noise)
0.05–0.2 100 0.04–0.2 80.7–100 -13.9 to
19.3
0.04–0.1 0.07–99.9 -67.8 to
67.8
-32.2 to
32.1
Good focal coverage (up to 60 %
noise)
0.04–0.2 100 0.04–0.2 88.8–100 -11.2 to
10.8
0.04–0.1 85.1–100 -11.1 to
11
-3.4 to 4.9
Poor focal coverage (up to 100 %
noise)
0.1–0.3 100 0.07–0.2 64.4–100 -35.6 to
27.6
0.07–0.2 0.02–99.9 -67.9 to
67.8
-32.3 to
32.2
Good focal coverage (up to 100 %
noise)
0.01–0.3 100 0.06–0.2 78.2–100 -19.8 to
21.8
0.06–0.2 71.9–100 -19.3 to
21.5
-6.8 to 8.9
Figure 7Null-trace MT results of the bootstrap amplitude resampling test. Upper row represents the results of tests for network configuration with the
uniform take-off angle on all azimuths. The lower row represents network configuration with the different take-off angles
206 G. Lizurek Pure Appl. Geophys.
(e.g., Lizurek and Wiejacz 2011; Stec 2007) and
several for events near Czorsztyn reservoir. The basic
mechanism solution description will be introduced
below with the examples of events.
USCB underground mining has a long, over
200 years, history. Currently, exploitation is per-
formed with longwall system on various depths from
300 to 1100 m on more than 20 mines (IS-EPOS
2016). The studies of mining-induced seismicity
showed two groups of events in USCB mines: first
connected directly with mining operations and second
with events connected with large discontinuities (e.g.,
Kijko et al. 1987; Idziak et al. 1991; Gibowicz and
Kijko 1994; Gibowicz and Lasocki 2001). This
bimodal character may result with complex and
multimodal magnitude distribution of mining seismic
events (Lasocki 2001). Stec (2007) called the first
group ‘‘mining’’ events and second ‘‘mining-
tectonic’’ according to full MT solutions. In nomen-
clature used in this work after the definition of Dahm
et al. (2013) the first group is called induced seis-
micity, while the second one is an example of
triggered seismicity. Induced events in USCB are
characterized by small shearing component in full
MT solution of about 10–20 % and very high non-DC
components with isotropic component from 20 to
50 %. The rupture orientations rarely follow any
preexisting local faults but are mainly connected with
excavation geometry and mining front orientation.
Location of these events was usually close to the
mining front and the magnitude is rarely above
ML = 3. The triggered events are characterized with
about 70 % of the shearing component in full MT
solution and the location of these events was close to
the tectonic discontinuities and usually far below the
mining level. The mechanism was mostly normal
Figure 8DC MT results of the bootstrap amplitude resampling test. Upper row represents the results of tests for network configuration with the uniform
take-off angle on all azimuths. The lower row represents network configuration with the different take-off angles
Vol. 174, (2017) Full Moment Tensor Inversion as a Practical Tool 207
faulting with some strike-slip component involved
and the nodal planes were in accord with the local
faults (Stec 2007 and literature therein).
Another site of the extensive underground mining
is LGCD, Southwestern Poland, where the copper ore
underground exploitation is carried out in three
mines: ‘‘Rudna’’, ‘‘Polkowice-Sieroszowice’’, and
‘‘Lubin’’. The ore bearing strata exploitation depth
ranges from 400 m in ‘‘Lubin’’ mine to 1250 in
‘‘Rudna’’ mine. Exploitation is performed in several
mining panels with pillar-chamber mining method.
(KGHM 2016). The three biggest events from LGCD
took place in 1977 ML = 4.5 (Gibowicz et al. 1979),
in 1987 event with ML = 4.3 (Gibowicz et al. 1989)
and 2013 with ML = 4.2 (Lizurek et al. 2015). The
moment tensor studies of LGCD events have been
carried out since early 1990’s (Krol et al. 1991;
Wiejacz 1992).
There are several hundred MT solutions from
various mines published since then, showing common
feature of high non-DC components in the solutions
of focal mechanisms of mining induced events from
LGCD (e.g., Gibowicz and Kijko 1994 and literature
therein). Mechanisms with implosive or explosive
component were reported for LGCD mines but usu-
ally no dominant fault plane was observed (e.g.,
Wiejacz 1992; Lizurek and Wiejacz 2011). Signifi-
cant multidimensional clustering of the smaller
events before the large seismic event with high non-
DC components was detected by Lizurek and Lasocki
(2014) within the chosen mining panel of ‘‘Rudna’’
mine. The significant role of the non-DC mechanisms
on the ground effects was also studied and proved by
Orlecka et al. (2014). Unlike USCB, all the seismicity
reported in the LGCD region is considered as a direct
mining-induced seismicity (Gibowicz and Kijko
1994). Even in case of 2013, ML = 4.2 event, which
occurred on the preexisting fault within the mine,
tectonic stress role in the seismogenic process cannot
be confirmed (Lizurek et al. 2015). In the following
study, Rudzinski et al. (2016) showed that the com-
plex rupture of such large mining seismic event
started on the fault, which acted as a weak zone rather
than a preexisting fault plane. The examples of
obtained tensors of main event and biggest after-
shocks are presented in Table 5. The dominance of
non-DC components in both aftershocks and main
shock supports the mining-induced origin of these
events.
The last anthropogenic seismic activity in Poland
is linked to the impoundment of Czorsztyn artificial
lake created on Dunajec river in south of Poland. It’s
filling ended in 1997. The reservoir of 234.5 million
cubic meters capacity is shallow, on average between
20 to 50 m of water column. Between 1995 and 2011
there were 60 events recorded in this area (1 event per
3 months in average), but since November 2011
seismic activity has increased up to about several
events per month. This region is tectonically active.
Czorsztyn Lake is situated in a border zone of Inner
and Outer Carpathians. Niedzica dam is located at the
eastern border of Orawa–Nowy Targ Basin, which is
Table 5
Examples of full MT solutions of March 19, 2013 ML = 4.2 Rudna Mine events and three of the largest aftershocks (Lizurek et al. 2015)
Event March 19, 2013 21:09 UTC March 19, 2013 21:13 UTC March 19, 2013 22:05 UTC March 19, 2013 23:15 UTC
Magnitude MW 3.7 1.9 2.1 2.3
MT components (Nm)
M11 -1.26 9 1014 -1.23 9 1011 -3.59 9 1011 -8.74 9 1011
M22 -7.10 9 1013 -2.08 9 1011 -1.99 9 1011 -9.75 9 1011
M33 4.46 9 1014 9.52 9 1011 1.70 9 1012 3.15 9 1012
M12 -6.76 9 1013 -2.88 9 1010 -1.40 9 1010 2.02 9 1011
M13 4.49 9 1012 1.22 9 1011 4.95 9 1011 4.14 9 1011
M23 -7.10 9 1013 1.19 9 1011 2.56 9 1011 1.18 9 1011
RMS 0.1 0.12 0.1 0.5
MT decomposition
ISO (%) 25 21 21 13
CLVD (%) 33 67 64 75
DC (%) 42 12 15 12
208 G. Lizurek Pure Appl. Geophys.
the most seismically active part of Polish Carpathians
with several earthquakes reported since 1717 and the
strongest events reported in 1990’s in the Krynica
vicinity with magnitude up to ML = 4.0 and early
2000’s in Podhale with the biggest event of ML = 4.5
(Guterch et al. 2005; Plesiewicz and Wiszniowski
2015). The seismicity of the area is considered as the
triggered seismicity with delayed response (Białon
et al. 2015). Currently, there are over 150 events
located in this area with ML from -0.6 to 2.4. There
are 23 moment tensor solutions calculated for the
events of 0.2 B ML B 2.1, Fig. 9 (IS-EPOS 2016).
The MT decomposition results (Fig. 10) confirm the
triggering origin of the seismicity in the area of
Czorsztyn lake. Shearing component is mostly dom-
inant part of the mechanisms, but the non-DC parts of
MT are observed—most of the events have at least
20 % of non-shearing components. This is in agree-
ment with the synthetic test results and suggests that
the events were rather triggered than purely induced.
This along the tectonic studies and historical seismic
activity of the broader vicinity in Orawa–Nowy Targ
Basin confirms hypothesis of the triggered seismicity
type.
Figure 9Focal mechanisms of 23 events triggered by Czorsztyn reservoir exploitation
Figure 10Histogram of DC component of full MT solutions for events near
Czorsztyn lake
Vol. 174, (2017) Full Moment Tensor Inversion as a Practical Tool 209
5. Conclusions
Full MT inversion is a practical tool for discrim-
inating natural and anthropogenic seismicity
especially for distinguishing triggered from purely
induced earthquakes. However, the method has some
limitations. The main limitation of the full MT
inversion with use of the first arrival P-wave dis-
placement amplitude comes from the focal sphere
coverage and its sensitivity to noisy data. In the case
of poor azimuthal and take-off angle coverage, the
results may become unreliable due to the high influ-
ence of noise (Fig. 6; Table 4). This was the case of
the full MT decomposition of the 2012 Jarocin
earthquake, where non-DC components dominated
the solution (Table 1). Therefore, the inversion for
the full MT should be compared with the null-trace
inversion for consistency. If a significant discrepancy
is discovered, additional tests for data quality should
be performed. Moreover, the interpretations of the
results should be taken with caution and should be
based on knowledge about tectonics and seismicity of
the area. There are also other than full MT models,
which may be more useful in obtaining more
stable results in case of small earthquakes such as the
shear-tensile crack model. This model works better in
retrieval of the DC vs non-DC content of the mech-
anism in case of the noisy data and poor focal
coverage (e.g., Sıleny 2009; Sıleny et al. 2014). In
case of complex rupture, the proper full MT decom-
position may also be crucial as it was proposed by
Rudzinski et al. (2016) for the Rudna mine excep-
tionally large event. The poor focal sphere coverage
is a by-product of the velocity model of the studied
area and the seismological network configuration.
Sites of the sparse seismicity may suffer due to both:
too approximate velocity model and sparse seismic
network. This is rather rare in case of the anthro-
pogenic seismicity, which is usually well covered by
seismic stations. In Polish underground mines both
the USCB and LGCD seismic networks are rather
dense (e.g., Stec 2007; Lizurek et al. 2015) and allow
to get proper focal sphere coverage with use of the
local velocity model. It is more complicated in case
of the surface networks. Rudzinski et al. (2016) and
Cesca et al. (2013) proved usefulness of the local and
regional surface networks in obtaining full MT with
the full waveform inversion. Regional surface net-
works were also proved to be robust for non-DC
component determination (e.g., Stierle et al. 2014b).
However, very dense networks of both short period
and broadband sensors with high quality recordings
and reasonably detailed velocity model including the
shallow subsurface layers are needed (Sen et al.
2013). The P-wave amplitude inversion was also
proved to be the more robust than the waveform
inversion method of the non-DC component calcu-
lation in case of surface sparse networks. The most
accurate values of the non-DC components were
obtained from the P-wave amplitude inversion (Fo-
jtikowa et al. 2010). The work of Białon et al. (2015)
and the catalog of MT solutions of the events from
the Czorsztyn Lake area (IS-EPOS 2016) show that
the amplitude inversion of first P-wave pulses may
also be a robust tool in case of surface network
recordings. Even having in mind the limitations of the
method the obtained results seem to be a good first
approximation of the full MT.
This work confirmed the Dahm et al. (2013) rec-
ommendation, that full MT solutions should be used
whenever it is possible in studies aiming at discrim-
ination of anthropogenic (including recognition of
induced and triggered types) and natural seismicity.
Following the results of the MT inversions of the
human-related and tectonic earthquakes from Poland,
the full MT analysis should be a significant part of the
discrimination workflow, but it cannot be treated as
the main and only input for such discrimination.
Acknowledgments
Grzegorz Lizurek have been partially supported by
project: IS-EPOS Digital Research Space of Induced
Seismicity for EPOS Purposes (POIG.02.03.00-14-
090/13-00), funded by the Polish National Center for
Research and Development as well as within statu-
tory activities No 3841/E-41/S/2016 of the Ministry
of Science and Higher Education of Poland. Figure 1
was prepared using the Generic Mapping Tools
package (Wessel et al. 2013). I wish to express my
gratitude to the Jan Sıleny and the anonymous
reviewer for their valuable comments, which consid-
erably improved this paper.
210 G. Lizurek Pure Appl. Geophys.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted
use, distribution, and reproduction in any medium, provided you
give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons license, and indicate if
changes were made.
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